Imported from javiarmesto/ALDC-AL-Development-Collection (skills/skill-migrate/SKILL.md). Install upstream with npx skills add javiarmesto/ALDC-AL-Development-Collection --skill skill-migrate. Copyright stays with the author.

Skill: AL Project Migration

Purpose

Plan and execute BC platform version upgrades: app.json configuration, breaking-change remediation, deprecated API replacement, event signature updates, upgrade codeunits for data migration, rollback strategy, and manifest regeneration.

When to Load

This skill should be loaded when:

• Upgrading an AL extension to a newer BC platform version (e.g., BC 23.x → 24.x)
• Fixing compilation errors after updating the runtime or platform property
• Replacing deprecated AL patterns (C/AL legacy, obsolete APIs)
• Updating event subscriber signatures after base-app changes
• Writing upgrade codeunits for schema changes or data migration
• Generating a full deployment package after migration

Core Patterns

For BC29 / AL18, first read AL18 capability checks when selecting new manifest, public-resource, isolation, testing or translation features. Apply only the sections needed by the requirement; distinguish announced capabilities from locally verified declarations. Keep BC28 configuration unchanged unless an upgrade is part of the approved task.

Pattern 1: App.json Platform Update

Update the three version-sensitive properties in app.json:

{
  "platform": "25.0.0.0",
  "runtime": "14.0",
  "application": "25.0.0.0",
  "dependencies": [
    {
      "id": "63ca2fa4-4f03-4f2b-a480-172fef340d3f",
      "name": "System Application",
      "publisher": "Microsoft",
      "version": "25.0.0.0"
    }
  ],
  "features": ["TranslationFile", "GenerateCaptions", "NoImplicitWith"]
}

Rules:

• platform — target BC platform version (major.minor.0.0)
• runtime — AL runtime version matching the target (see runtime matrix)
• application — must match or be compatible with target platform
• Resolve each dependency by identity, minimum version, target runtime and required APIs; do not require every library version to numerically match the application version.
• Add new features flags required by the target runtime (e.g., NoImplicitWith from runtime 11.0+)

Pattern 2: Deprecated Code Replacement

Replace legacy patterns with modern equivalents:

// ❌ Deprecated — C/AL style
Record.FIND('-');
Record.FINDSET(TRUE, TRUE);
IF Record.FINDFIRST THEN;
Record.INIT;
Record.INSERT;

// ✅ Modern — AL patterns
Record.FindSet();
Record.FindSet(true, true);
if Record.FindFirst() then;
Record.Init();
Record.Insert(true);

// ❌ Deprecated — WITH statement (removed in NoImplicitWith)
with SalesHeader do begin
    "Document Type" := "Document Type"::Order;
    "Sell-to Customer No." := CustomerNo;
    Insert(true);
end;

// ✅ Modern — explicit record reference
SalesHeader."Document Type" := SalesHeader."Document Type"::Order;
SalesHeader."Sell-to Customer No." := CustomerNo;
SalesHeader.Insert(true);

// ❌ Deprecated — TextConst (runtime < 6.0)
CustomerNotFoundErr@1000 : TextConst 'ENU=Customer %1 not found.';

// ✅ Modern — Label
var
    CustomerNotFoundErr: Label 'Customer %1 not found.';

Pattern 3: Event Signature Migration

When base-app events add or change parameters between versions:

// BC 23.x subscriber — 3 parameters
[EventSubscriber(ObjectType::Codeunit, Codeunit::"Sales-Post",
                 OnBeforePostSalesDoc, '', false, false)]
local procedure OnBeforePost(
    var SalesHeader: Record "Sales Header";
    CommitIsSuppressed: Boolean;
    var IsHandled: Boolean)
begin
    // ...
end;

// BC 24.x — same event now has 4 parameters (new PreviewMode added)
[EventSubscriber(ObjectType::Codeunit, Codeunit::"Sales-Post",
                 OnBeforePostSalesDoc, '', false, false)]
local procedure OnBeforePost(
    var SalesHeader: Record "Sales Header";
    CommitIsSuppressed: Boolean;
    PreviewMode: Boolean;
    var IsHandled: Boolean)
begin
    // ...
end;

Migration steps:

1. Build with al_build — signature mismatches produce AL0482 errors
2. Use al_get_object_definition to inspect the new publisher signature
3. Update parameter list to match exactly (name, type, order)
4. Re-verify with al_build

Pattern 4: Obsolete Object Handling

Handle objects marked ObsoleteState = Removed in the target version:

// Step 1: Find usage of removed objects
// al_search_objects — search for the obsolete table/page/codeunit

// Step 2: Replace with the designated successor
// Before (removed in BC 24):
// Codeunit 80 "Sales-Post (Yes/No)" — ObsoleteState = Removed
// After:
Codeunit.Run(Codeunit::"Sales-Post", SalesHeader);

// Step 3: Check ObsoleteReason for migration guidance
// ObsoleteReason typically says: "Use codeunit X instead"

Process:

1. Compile → collect all AL0503 (removed) and AL0432 (pending) warnings
2. For Removed — must fix before compilation succeeds
3. For Pending — fix proactively to avoid future breaks
4. Check release notes for each removed object's replacement

Pattern 5: Upgrade Codeunit (Data Migration)

Use upgrade codeunits to transform data when schema changes between versions:

codeunit 50100 "Contoso Data Upgrade"
{
    Subtype = Upgrade;

    trigger OnUpgradePerCompany()
    var
        Module: Info;
    begin
        Module.DataVersion(1);      // check data version tracking
        MigrateCustomerLoyaltyData();
        SplitAddressFields();
    end;

    trigger OnValidateUpgradePerCompany()
    begin
        // Pre-upgrade validation — runs before OnUpgradePerCompany
        VerifyDataIntegrity();
    end;

    local procedure MigrateCustomerLoyaltyData()
    var
        Customer: Record Customer;
        ContosoLoyalty: Record "Contoso Loyalty Entry";
        UpgradeTag: Codeunit "Upgrade Tag";
    begin
        if UpgradeTag.HasUpgradeTag(GetLoyaltyMigrationTag()) then
            exit;

        // Migrate data from old field to new table
        Customer.SetFilter("Contoso Legacy Points", '>0');
        if Customer.FindSet() then
            repeat
                ContosoLoyalty.Init();
                ContosoLoyalty."Customer No." := Customer."No.";
                ContosoLoyalty.Points := Customer."Contoso Legacy Points";
                ContosoLoyalty."Entry Date" := WorkDate();
                ContosoLoyalty.Insert();
            until Customer.Next() = 0;

        UpgradeTag.SetUpgradeTag(GetLoyaltyMigrationTag());
    end;

    local procedure GetLoyaltyMigrationTag(): Code[250]
    begin
        exit('CONTOSO-LOYALTY-MIGRATION-20260301');
    end;
}

Upgrade codeunit rules:

• Subtype = Upgrade — BC runs these automatically during app upgrade
• Use UpgradeTag to ensure idempotency — never run migration twice
• OnValidateUpgradePerCompany runs first — validate data before transforming
• OnUpgradePerCompany runs per company — do the actual migration
• Always test with a copy of production data before deploying
• For large datasets, use SelectLatestVersion() and batch processing

Pattern 6: Rollback Strategy

Document and prepare rollback before executing migration:

## Rollback Plan — {Project} Migration v{X} → v{Y}

### Pre-Migration Checklist
- [ ] Git branch created from stable tag: `git checkout -b migration/vX-to-vY vX.0.0`
- [ ] Database backup taken and verified
- [ ] Extension .app file of current version archived
- [ ] Rollback tested in sandbox environment

### Rollback Procedure
1. **Code rollback**: `git checkout vX.0.0` — restore previous version
2. **Extension rollback**: Uninstall new version, install archived .app
3. **Data rollback** (if upgrade codeunit ran):
   - Restore database from pre-migration backup
   - OR run compensating downgrade codeunit (if written)
4. **Verify**: Run smoke tests on restored environment

### Point of No Return
⚠️ After these actions, rollback requires database restore:
- Upgrade codeunits that DELETE data
- Schema changes that DROP columns
- External system notifications sent

Rollback rules:

• Always create a rollback plan BEFORE starting migration
• Tag the pre-migration commit: git tag vX.0.0-pre-migration
• Archive the current .app file alongside the plan
• Test rollback in sandbox — never assume it works
• If upgrade codeunit is destructive (deletes data), document the point of no return

Workflow

Step 1: Pre-Migration Assessment

1. Backup: Ensure source control is up to date (git status clean)
2. Download current symbols: al_downloadsymbols
3. Document dependencies: al_packages — list loaded packages with current versions
4. Review release notes: Check BC target version breaking changes
5. Create migration plan in .github/plans/{project}-migration.md

PAUSE — wait for user approval before modifying files.

Step 2: Update Configuration

1. Update app.json (Pattern 1) — platform, runtime, application, dependencies, features
2. Download new symbols for target version
3. Build: al_build — collect all errors

Step 3: Fix Compilation Errors

Prioritize by error type:

1. AL0503 (Removed objects) → Pattern 4
2. AL0482 (Event signature mismatch) → Pattern 3
3. AL0432 (Deprecated usage) → Pattern 2
4. Other errors → case-by-case analysis

For each fix, verify with incremental build.

Step 4: Regenerate and Validate

1. Update the manifest (app.json) — no agent tool; edit directly (or via the VS Code command)
2. Full build: al_build — zero errors, zero new warnings; al_build also produces the .app package
3. Run existing tests to verify no regressions

Step 5: Post-Migration

1. Update CHANGELOG with migration notes
2. Tag the commit with new version
3. Test in sandbox environment before production

Version-Specific Notes

References

• Choosing the Runtime Version
• Breaking Changes per Release
• ObsoleteState Property
• App.json Properties
• NoImplicitWith Feature
• Upgrade Codeunits
• Upgrade Tags

Constraints

• This skill covers version migration planning, breaking-change remediation, and configuration updates
• Do NOT modify base BC objects — extension-only changes
• Do NOT skip the pre-migration backup and assessment step
• Do NOT combine migration with feature development — migrate first, then develop
• Always create a migration plan and obtain approval before modifying files
• Event debugging → skill-debug.md | Performance after migration → skill-performance.md | Test verification → skill-testing.md